One-way clutch with resilient ring and starter using the same

ABSTRACT

In a one-way clutch used in a starter for engines, a locking concave for locking a roller thereto is formed on a roller-moving surface of one clutch member having a peripheral surface facing a peripheral surface of the other clutch member having a wedge-shaped groove for accommodating the roller. A resilient member for disengaging the roller from the locking concave at the time of overrunning is accommodated in an annular groove, thus urging the roller radially outwardly. The roller is prevented from colliding with the locking concave at the time of overrunning so that vibrations and noise are not generated.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priorities of Japanese PatentApplications No. 8-37605 filed on Feb. 26, 1996 and No. 8-64519 filed onMar. 21, 1996, the contents of which are incorporated herein byreference.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priorities of Japanese PatentApplications No. 8-37605 filed on Feb. 26, 1996 and No. 8-64519 filed onMar. 21, 1996, the contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a one-way clutch for transmitting atorque in one direction and a starter using the one-way clutch.

2. Related Art

As a clutch for use in a starter, a roller type one-way clutch isdisclosed in Japanese Utility Model Publication No. 59-26107. In thisone-way clutch, each roller accommodated in a wedge-shaped space formedbetween an outer member and an inner member bites into the gap betweenthe outer member and the inner member when the roller shifts to theshallow side of the wedge-shaped space, thus transmitting a torquebetween the two members. When the roller shifts to the deep side of thewedge-shaped space, the roller does not contact the outer member and theinner member simultaneously. In this manner, torque transmission betweenthe outer member and the inner member is prevented.

In particular, it is proposed that when a transmitted torque exceeds apredetermined value, the outer member (or inner member) rotates slidablythrough the roller to prevent excess torque from being transmitted.

In this clutch, however, due to a slight fluctuation of the length ofthe gap between the outer member and the inner member at the end of theshallow side of the wedge-shaped space, the biting amount of the rolleron the outer member (or inner member) changes. As the result, a maximumtransmission torque amount fluctuates greatly.

In order to solve this problem, Japanese Patent Application No. 6-213707which corresponds to U.S. application Ser. No. 08/381,498 filed on Jan.31, 1995 proposes another roller type one-way clutch in which a lockingconcavity is formed on the peripheral surface of either an outer memberor an inner member is proposed. A wedge-shaped groove accommodating aroller is formed on the inner peripheral surface of the outer member,and locking grooves for locking the roller are formed on the peripheralsurface of the inner member. The roller engages one of the lockinggrooves during torque transmission. When a torque greater than apredetermined value is applied to the outer member, the roller shifts tothe next locking groove.

In the one-way clutch provided with the locking concavity, however, ashock is applied to the roller due to the irregularities of the lockingconcavity at the time of overrunning. As a result, there is apossibility that the roller, the inner member, and the outer member aredamaged, and noises and vibrations are generated.

Further, in the conventional roller type one-way clutch having nolocking concavities, the maximum transmission torque amount depends onthe friction coefficient between the cylindrical roller-moving surfaceand the roller. Thus, it is not easy to adjust the friction coefficientand prevent the changes thereof with the elapse of time. Further, if thefriction coefficient is too great, abrasion of the roller and the likeincreases, whereas if the friction coefficient is too small to reducethe abrasion thereof, the maximum transmission torque cannot be obtainedas desired.

SUMMARY OF THE INVENTION

The present invention has an object of providing a one-way clutchcapable of preventing damage of rollers while it secures a preferabletorque transmission characteristic.

The present invention has another object of providing a one-way clutchcapable of suppressing generation of noises and vibrations.

The present invention has a further object of providing a starter usingthe one-way clutch.

According to the present invention, a locking concavity which engages aroller is formed on either the inner peripheral surface of a clutchouter member or on the peripheral surface of a clutch inner member. Aresilient member is disposed to bias the roller in a radial directionthereof. At a normal torque transmission time, the roller is positionedat a shallow side of the wedge-shaped groove and contacts the peripheralsurface of the locking concavity, thus transmitting a torque from theouter member to the inner member and vice versa. During overrunning, theresilient member shifts the roller to a deep side of the wedge-shapedgroove, thus disengaging the roller from the locking concavity.

The resilient member urges the roller toward the wedge-shaped groove,namely, outwardly in the radial direction thereof. Consequently, eventhough shocks or vibrations are applied or the degree of a transmittedtorque changes rapidly, the roller can be prevented from being shaken ormoving out from the wedge-shaped groove. In this manner the torquetransmission can be accomplished without too much noises.

Preferably, the locking concavity is formed on the inner member so thata centrifugal force is generated in the resilient member during a highspeed rotation. Thus, there is an increase in the force of the resilientmember of urging the roller in the centrifugal direction, namely, in thedirection in which the roller disengages from the locking concavity incorrespondence with the generation of the centrifugal force in theresilient member. Accordingly, the resilient member disengages theroller smoothly from the locking concavity by that much, thus reducingthe degree of abrasion of the roller and the generation of abnormalsounds.

Preferably, the resilient member is made of a resilient metal ringaccommodated in an annular groove formed on the other of the innerperipheral surface of the outer member and the peripheral surface of theinner member so that resiliency can be imparted to a plurality ofrollers provided thereon although the one-way clutch has a simpleconstruction.

Preferably, the radial depth of the annular groove from the deepestbottom of the locking concavity is smaller than the thickness of theresilient ring so that the roller is kept radially above the deepestbottom of the locking concavity when the roller is received in thelocking concavity during torque transmission.

Preferably, at least one pair of the resilient members is formed suchthat the resilient member contacts both sides of the peripheral surfaceof the roller. Thus, a partial abrasion of the roller can be prevented.

Preferably, the annular groove is formed to have a radial depthgradually becoming deeper from an axial end side of the inner member andonly an axially inside part of the resilient ring contacts an axial endpart of the resilient ring. Thus, only the axially inside part isresiliently deformed in the annular groove.

Preferably, the one-way clutch is used in a starter for an engine toprevent the overrunning of the starter provided with an epicyclic gearreduction mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readwith reference to the accompanying drawings, in which:

FIG. 1 is a partial sectional view showing a starter using a one-wayclutch according to a first embodiment of the present invention;

FIG. 2 is a sectional view showing a normal torque transmission state ofthe one-way clutch according to the first embodiment;

FIG. 3 is a sectional view showing an overrunning state of the one-wayclutch according to the first embodiment;

FIG. 4 is a perspective view showing an inner member of the one-wayclutch according to the first embodiment;

FIG. 5 is an enlarged perspective view showing a part of the innermember shown in FIG. 4;

FIG. 6 is a partial sectional view showing a front half of a starterusing a one-way clutch according to a second embodiment of the presentinvention;

FIG. 7 is a sectional view showing a pinion shown in FIG. 6;

FIG. 8 is a sectional view showing a part of a one-way clutch accordingto a third embodiment of the present invention;

FIG. 9 is a sectional view showing a clutch-connected state of a one-wayclutch according to a fourth embodiment of the present invention;

FIG. 10 is a sectional view showing an overrunning state of the one-wayclutch according to the fourth embodiment;

FIG. 11 is a sectional view showing a one-way clutch according to afifth embodiment of the present invention;

FIG. 12 is a partial sectional view showing a starter using a one-wayclutch according to a sixth embodiment of the present invention;

FIG. 13 is a sectional view showing a torque transmission state of theone-way clutch according to the sixth embodiment;

FIG. 14 is a sectional view showing an overrunning state of the one-wayclutch according to the sixth embodiment;

FIG. 15 is a partial sectional view showing a starter using a one-wayclutch according to a seventh embodiment of the present invention;

FIG. 16 is a sectional view showing the one-way clutch according to theseventh embodiment; and

FIG. 17 is a partial sectional view showing a starter using a one-wayclutch according to an eighth embodiment of the present invention.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowin detail with reference to the accompanying drawings in which samereference numerals are used to denote the same or equivalent parts.

(First Embodiment)

In FIGS. 1 through 5, a starter has a housing 1 and a center casing 2fixed to the housing 1 and accommodating an epicyclic gear reductionmechanism 3. A driving shaft (output shaft of starter) is rotatablysupported by the housing 1 at its front end and by the center casing 2through bearings 40 and 41, respectively. A concavity is formed at therear end of the driving shaft 4. The concavity supports the front end ofa rotation shaft 42 of a motor rotatably along the axis of the drivingshaft 4 through a bearing.

A sun gear 31 of the epicyclic gear reduction mechanism 3 is formed atthe front end of the rotation shaft 42. Planetary gears 32 engage thesun gear 31 such that the planetary gears 32 revolve around the sun gear31. The planetary gears 32 are rotatably supported by respective pins 33through respective bushings. The pins 33 are fixed to a large-diameterportion 43 formed at the rear end of the driving shaft 4. An internalgear 34 made of resin and surrounding the planetary gears 32 is providedsuch that the internal teeth 340 of the internal gear 34 are meshed withthe planetary gears 32. The internal gear 34 comprises alarge-cylindrical portion 341 having the internal teeth 340 formedthereon, a small-cylindrical portion 342 positioned in front of andadjacent to the large-cylindrical portion 341, and a wall portion 343disc-shaped and connecting the large-cylindrical portion 341 and thesmall-cylindrical portion 342 with each other, thus having a steppedcylindrical shape. The small-cylindrical portion 342 constitutes anouter member (clutch outer member) of a one-way clutch 5.

The center casing 2 comprises a large-cylindrical portion 21, an endwall portion 22 which closes the front end of the large-cylindricalportion 21, and a small-cylindrical portion 23 projecting rearwardaxially from the radial inner end of the end wall portion 22. Thesmall-cylindrical portion 23 constitutes an inner member (clutch innermember) of the one-way clutch 5 and serves as a bearing cylindricalportion supporting the driving shaft 4.

A pinion 6 is mounted on the driving shaft 4 by means of a spline-fit-insuch that the pinion 6 is nonrotatable relative to the driving shaft 4and movable relative thereto in the axial direction thereof. A piniongear 61 capable of engaging a ring gear 7 is formed on the peripheralsurface of the pinion 6 at the front end thereof. Reference numeral 62denotes a spline-fit-in portion, and 63 denotes a bearing.

A magnet switch 8 is fixed to an upper portion of the housing 1. When aplunger (not shown) of the magnet switch 8 moves rearward (right-handdirection in FIG. 1), the pinion 6 is moved forward through a lever 82.

As shown in FIGS. 2 and 3, a predetermined number of wedge-shapedgrooves 50 is formed at predetermined angular intervals on the innerperipheral surface of the outer member 342. Each wedge-shaped groove 50accommodates a roller (clutch roller) 51 and a spring (clutch spring) 52as a pair. The bottom surface of the wedge-shaped groove 50 is concavecontinuously deeply from the left-hand side to the right-hand side inthe Figures. An end wall for locking the roller 51 is formed at each ofboth ends of the wedge-shaped groove 50. The roller 51 is urged to theshallow side of the wedge-shaped groove 50 by the spring 52 to bepressed in a radially inward direction.

Locking concavities 53, the number of which is more than that of therollers 51 are circumferentially formed at regular intervals on theperipheral surface (roller-moving surface) 230 of the inner member 23.As shown in FIGS. 4 and 5 further, a pair of annular grooves 54 areformed on the entire peripheral surface 230 of the inner member 23. Eachannular groove 54 accommodates a ring (resilient member) 55 made ofhighly-resilient metal and is formed deeper than the locking concavity53. The inner diameter of the ring 55 is larger than the diameter of thegroove 54, and the thickness of the ring 55 is larger than the radialdepth between the surface of the groove 54 and the deepest bottom of theconcave 53. Thus, the outer periphery of the ring 55 becomes higher thanthe top 230 (C) of the inner member 23.

When the outer member 342 rotates clockwise relative to the inner member23, as shown in FIG. 2, the roller 51 curves the ring 55 radiallyinwardly, thus contacting the end wall of the wedge-shaped groove 50 atits shallow side and the peripheral surface of the locking concavity 53at its shallow side. Consequently, the clockwise normal torque of theouter member 342 is transmitted from the bottom surface and the end wallof the wedge-shaped groove 50 at the shallow side thereof to mainly theend of the peripheral surface of the locking concavity 53, at itsshallow side, of the inner member 23 through the roller 51. Because theinner member 23 is a fixed member, the torque is transmitted from theplanetary gears 32 to the driving shaft 4 by restricting the rotation ofthe outer member 342. Accordingly, in the transmission of the normaltorque, the ring 55 is curved and kept above the deepest bottom of theconcavity 53, thus pressing the roller 51 against the bottom surface ofthe wedge-shaped groove 50 to prevent the roller 51 from being shakenand moved out from the wedge-shaped groove 50. In addition, the ring 55allows the roller 51 to move away from the locking concavity 53 rapidlyat the time of overrunning and the application of an excess torque whichwill be described later. In the transmission of the normal torque,rotation of the outer member 342, the ring 55 is curved greatly. Thus,the ring 55 follows the shift of the roller 51, thus rotating in theannular groove 54 relative to the inner member 23.

In this embodiment, the outer diameter of the ring 55 is set to beslightly larger than that of the roller moving surface or top 230 of theinner member 23. That is, the outer circumference of the ring 55 liesradially above the top C of the locking concavity 53. Consequently, whenan overrunning occurs and when the outer member 342 rotatescounterclockwise relative to the inner member 23, as shown in FIG. 3,the roller 51 moves to the deep side of the wedge-shaped groove 50 whilethe roller 51 is compressing the spring 52 by the frictional resistanceto the ring 55 and a centrifugal force applied thereto, thus eliminatingthe curve of the ring 55 and moving out from the locking concavity 53radially outwardly. As a result, the roller 51 slides on the outerperipheral surface of the ring 55 in contact therewith, and the ring 55rotates smoothly relative to the inner member 23, thus preventing thetorque transmission between the outer member 342 and the inner member23.

When an excess torque is applied in the torque transmission direction,i.e., when the resistance to the rotation of the rotary member, namely,when the resistance to the rotation of the outer member 342 or the innermember 23 at the driven side is great, the roller 51 is pressed againstthe outer member 342 made of resin and resiliently deforms radiallyoutwardly, and the roller 51 moves past the peripheral surface of thelocking concavity 53. As a result, the roller 51 and the outer member342 rotate (idle) clockwise relative to the inner member 23, thuspreventing the transmission of a torque higher than a predeterminedlevel. At this time, each roller 51 drops into the corresponding lockingconcavity 53 sequentially. Because the roller 51 is always urgedradially outwardly by the curved part of the ring 55, the roller 51 isnot greatly shaken radially. Thus, a high degree of noise is notgenerated.

Because at least a pair of the rings 55 is formed axially at apredetermined interval, the ring 55 prevents one side of the roller 51from dropping below the other side thereof and thus a partial abrasionof the roller 51 can be prevented.

Upon start of rotation of the sun gear 31 due to application ofelectricity to the motor, the planetary gears 32 of the epicyclic gearreduction mechanism 3 revolve around the sun gear 31 and thus thedriving shaft 4 and the pinion 6 rotate. When the magnet switch 8 causesthe pinion 6 to move forward through the lever 82, the pinion 6 engagesthe ring gear 7 to drive the engine. At this time, the torque in thenormal torque transmission direction is applied to the internal gear 34from the planetary gears 32. The internal gear 34 is kept stationarybecause the inner member 23 is stationary. When resistance to therotation of the driving shaft 4, namely, resistance to the rotation ofthe planetary gears 32 around the sun gear 31 becomes great due to are-start which is made immediately after a failure of the engagementbetween the pinion 6 and the ring gear 7 although the sun gear 31 isstill in inertial rotation, the rotating planetary gears 32 drive theinternal gear 34. Consequently, the outer member 342 rotates (forciblyrotated in the torque transmission direction), thus preventing thegeneration of an excessive shock from occurring by the engagementbetween the pinion 6 and the ring gear 7. Upon start of the engine, thering gear 7 rotates the driving shaft 4 through the pinion 6 in therotational direction of the sun gear 31 at a speed higher (overrunningstate) than that of the sun gear 31. As a result, because the one-wayclutch 5 becomes free as described above, the motor can be preventedfrom being rotated at a high speed.

In this embodiment, when an overrunning state occurs, a centrifugalforce is applied to the roller 51 which starts to rotate together withthe internal gear 34. As a result, the roller 51 is shifted in theclutch connection-release direction along the wedge-shaped groove 50.Therefore, the shift to the overrunning state can be smoothlyaccomplished.

(Second Embodiment)

The second embodiment is substantially identical to that of the firstembodiment (FIG. 1) except that the mounting position of the one-wayclutch of the second embodiment is altered from that of the one-wayclutch of the first embodiment.

As shown in FIGS. 6 and 7, a pinion member 6 having a pinion tube 63made of metal and a spline tube 64 located behind the pinion tube 63 isfitted into the driving shaft 4. A pinion gear 61 is formed at the frontend of the peripheral surface of the pinion tube 63. The rear part ofthe pinion tube 63 constitutes the inner member of a one-way clutch 5.The pinion tube 63 is axially movable relative to the driving shaft 4and rotatable relative thereto through a bearing. A large-diameter frontpart 641 of the spline tube 64 constitutes the outer member of theone-way clutch 5, whereas a rear part of the spline tube 64 is mountedon the driving shaft 4 by a spline-fit-in at a spline-fit-in portion 45of the driving shaft 4. Similarly to the first embodiment, a roller 51,a ring 55, a wedge-shaped groove (not shown), a locking concavity (notshown), and a pair of annular grooves 54 are formed in the gap, betweenthe outer member 641 and the inner member 631, in the radial directionthereof. There are provided a cover 642 fixed to the periphery of theouter member 641 and a washer 643 closing the opening of the outermember 641. Another washer 644 positioned in front of and adjacent tothe washer 643 is fitted in annular grooves, thus preventing the roller51 and grease from moving to the outside and securing shift thereoftogether with the outer member 641 and the inner member 631 in the axialdirection of the driving shaft 4.

(Third Embodiment)

The third embodiment is substantially the same as the first embodimentexcept that an inner member is formed integrally with an internal gear34 (FIG. 1). As shown in FIG. 8, an outer member is formed integrallywith the center casing 2. Wedge-shaped groove 50 accommodating theroller 51 and the spring 52 is formed on the inner member 23. A lockingconcavity 53 is formed on the outer member 65.

(Fourth Embodiment)

The fourth embodiment is a modification of the second embodiment shownin FIGS. 6 and 7. That is, merely the shape of the annular groove 54 ofthe one-way clutch 5 shown in FIG. 7 and that of the ring 55 aremodified.

In this embodiment, as shown in FIGS. 9 and 10, a pair of annulargrooves 54 is formed at both axial ends of the peripheral surface of aninner member 631 in such a manner that the annular grooves 54 confrontboth ends of a roller 51. In the sectional view of the annular grooves54 in the axial direction of the one-way clutch 5, the annular grooves54 are concave gradually deeper from both axial ends of the inner member631 to its center. Ring 55 made of resilient metal are cylindricallyplate-shaped and fitted in the annular grooves 54. The inner peripheralsurface of the rings 55 are in close contact with both ends of the innermember 631. A locking concavity 53 is formed at the center of the innermember 631.

As shown in FIG. 9, in a torque transmission state, because the roller51 is positioned at the shallow side of a wedge-shaped groove 50 of theouter member 641, the roller 51 shifts radially inwardly, thus engaginga locking concavity 53 of the inner member 631, whereas the ring 55 iscurved radially inwardly, thus urging the roller 51 radially outwardly.In an overrunning state, as shown in FIG. 10, because the roller 51 ispositioned at the deep side of the wedge-shaped groove 50 of the outermember 641, the roller 51 shifts radially outwardly and is urgedradially outwardly by the ring 55. As a result, the roller 51 is kept ina state in which it is in disengagement from the locking concavity 53.Thus, the roller 51 can be prevented from engaging the locking concavity53.

(Fifth Embodiment)

The fifth embodiment is a modification of the one-way clutch of thefirst embodiment.

As shown in FIG. 11, an epicyclic gear reduction mechanism 3 of thisembodiment is similar to that provided with the one-way clutch shown inFIG. 1 except that the one-way clutch is installed between the innerperipheral surface of a planetary gear-supporting cylinder correspondingto the large-diameter portion 43 shown in FIG. 1 and the peripheralsurface of a driving shaft 4 in which the planetary gear supportingcylinder 43 is fitted.

In more detail, the driving shaft 4 is rotatably supported by a centercasing not shown in FIG. 11 through a bearing, and an internal gear 34is rotatably supported by the driving shaft 4 through a bearing.

Planetary gears 32 engaging a sun gear of an armature rotation shaft 42are rotatably supported by respective pins 33 through respectivebushings, and the pins 33 are inserted into the planetarygear-supporting cylinder 43 under pressure. The planetary gearsupporting cylinder 43 is rotatably fitted in the rear end of thedriving shaft 4. The inner peripheral surface of the planetary gearsupporting cylinder 43 has a wedge-shaped groove 51, thus constitutingan outer member. Similarly to FIG. 9, a locking concavity 53 is formedat the center of the rear end of the driving shaft 4 (an inner member)in the axial direction thereof. An annular groove 54 in which a ring 55is fitted is formed at both axial sides of the inner member.

A ring plate 47 is fixed to the cylinder 43 for preventing the roller 51or the like from being moved out from the wedge-shaped groove 50.

(Sixth Embodiment)

The sixth embodiment is a modification of the fourth embodiment shown inFIGS. 9 and 10.

As shown in FIG. 12, two resilient metal rings 55 are disposed tocontact the axial end parts of a roller 51, thus preventing inclinationof the roller 51 and assuring stable operation of the one-way clutch 5.About one half width (axial length) of each ring 55 extends axiallyoutside from the end face of the roller 51. The radially outer peripheryof the extended part of the ring 55 is normally or under the stationarycondition in contact with the radially inner peripheries of a side wall645 of an outer member 641 (spline tube 64) and a plate washer 643. Thisarrangement restricts deformation of the ring 55 caused by thecentrifugal force at the time of overrunning state, while assuring theone-way clutch operation. The restriction of the inner peripheries ofthe side wall 645 and the washer 643 help the ring 55 to be placed inposition with its radial center becoming coaxial with a driving shaft 4,so that the roller 51 may be placed evenly axially in a wedge-shapedgroove 50 and that the inner member 631 and the outer member 641 may bekept in the coaxial relation to each other at the overrunning state.With the outer periphery of the ring 55 being in contact with the sidewall 645 and the washer 643, even when the inner member 631 is driven byan engine in the overrunning state and rotates at higher speeds, theouter member 641 driven by a starter motor rotates idly. Therefore, theinfluence of the centrifugal force is reduced and the abnormaldeformation of the ring can be prevented.

Further as shown in FIGS. 12 and 13, the ring 55 is placed in an annulargroove 54 of the inner member 631 so that the radial outer periphery ofthe ring 55 normally resides between the radially highest part (top) Cand the radially lowest part (bottom) B of the locking concavity 53. Atthe time of overrunning, the ring 55 having been bent or curved by theroller 51 received in the locking concavity 53 during the torquetransmission state (engine starting operation state) tends to move theroller 51 radially outwardly by its own resiliency, thereby disengagingthe roller 51 from the locking concavity 53. As a result, the contactresistance between the inner member 631 and the outer member 641 isreduced, the collision of the roller 51 with the locking concavity 53can be reduced and the movement of the roller 51 can be stabilized,resulting in reduction of friction noise during overrunning. Further,not only can the deformation of roller 51 be reduced but also fatigue ofa spring 52 caused by the movement of the roller 51 can be reduced.

(Seventh Embodiment)

The seventh embodiment is a modification of the sixth embodiment shownin FIGS. 12 through 14.

In this embodiment, as shown in FIG. 15, a resilient annular ring 55 ispress-fitted to an inner member 631 for rotation therewith. That is,about one half width of each ring 55 is fixed to the outer periphery ofthe inner member 631 and the remaining half is held above an annulargroove 54 to be curved by a roller 51 radially inwardly during thetorque transmission state. Further as shown in FIG. 16, the radiallyouter periphery of the ring 55 normally resides radially outside thehighest part (top) C of the locking concavity 53.

According to this embodiment, only about one half of the ring 55, i.e.,the axially inside part contacting the axial end part of the roller 51,resiliently deforms between the torque transmission state and theoverrunning state with the axially outside part of the ring 55 beingcontinuously fixed to the inner member 631. Therefore, even when thecentrifugal force exerted on the ring 55 at the time of overrunning, theannular ring 55 can keep its ring shape and is not deformedeccentrically, thus preventing unstable operation of the roller 51.Further, with the outer periphery of the ring 55 being maintained abovethe highest part C of the locking concavity 53, the roller 51 can movein the wedge-shaped groove 51 without hitting or colliding with thehighest part C.

(Eighth embodiment)

The eighth embodiment is a modification of the seventh embodiment shownin FIGS. 15 and 16.

In this embodiment, as shown in FIG. 17, each resilient metal ring 55 isformed with a U-shaped cross section. The radially inner periphery andthe radially outer periphery of the ring 55 is fixed to the annulargroove of the inner member 631 and is held in sliding contact with theroller 51, respectively. The ring 55 may alternatively be formed in adisk spring shape so that its small diameter side is fixed to the innermember 631 and its large diameter side is held in sliding contact withthe outer member 641.

The foregoing embodiments are not restrictive but may be modifiedfurther without departing from the spirit and scope of the invention.

What is claimed is:
 1. An apparatus comprising:an outer member and aninner member rotatable relative to each other and opposed to each otherwith a predetermined interval in a radial direction therebetween; awedge-shaped groove formed on one of an inner peripheral surface of theouter member and an outer peripheral surface of the inner member suchthat the depth of the wedge-shaped groove increases from one side to theother side in a circumferential direction; an annular groove formed onanother of the inner peripheral surface of the outer member and theouter peripheral surface of the inner member; a roller movablyaccommodated in the wedge-shaped groove for connecting the outer memberand the inner member with each other at a shallow side of thewedge-shaped groove so as to transmit a torque and for disconnecting theouter member and the inner member from each other at a deep side of thewedge-shaped groove; a locking concavity formed on said another of theinner peripheral surface of the outer member and the outer peripheralsurface of the inner member for locking the inner roller thereto whenthe outer member and the inner member are connected with each other; anda resilient member disposed on said another of the inner peripheralsurface of the outer member and the outer peripheral surface of theinner member for shifting the roller to a position at which the rollerdoes not contact a radial top of the locking concavity when the outermember and the inner member are disconnected from each other.
 2. Theapparatus according to claim 1, wherein:the resilient member is disposedto keep the roller from a radial bottom of the locking concavity whenthe roller is received in the locking concavity so that the outer memberand the inner member are connected with each other.
 3. The apparatusaccording to claim 1, wherein:the locking concavity is formed on theinner member circumferentially.
 4. The apparatus according to claim 1,wherein:the roller is disposed to disengage from the locking concavitydue to a resiliency of the resilient member when a torque greater than apredetermined amount is applied in a torque transmission direction. 5.The apparatus according to claim 1,wherein the resilient member includesa resilient ring accommodated in the annular groove.
 6. The apparatusaccording to claim 1, further comprising at least one additionalresilient member, the resilient member and the at least one additionalresilient member forming a plurality of resilient members and beingdisposed at a plurality of locations spaced apart from one another inthe axial direction of the outer member and the inner member such thatthe plurality of resilient members contact at least both axial sides ofthe roller.
 7. The apparatus according to claim 1, wherein:at least oneadditional wedge-shaped groove is formed on the same surface as thewedge-shaped groove, the wedge-shaped groove and the at least oneadditional wedge-shaped groove forming a plurality of wedge-shapedgrooves, each groove in said plurality of wedge-shaped grooves having acorresponding roller movably accommodated therein; at least oneadditional locking concavity is formed on said another of the innerperipheral surface of the outer member and the outer peripheral surfaceof the inner member, the locking concavity and the at least oneadditional locking concavity forming a plurality of locking concavities;and the number of the locking concavities in said plurality of lockingconcavities is greater than the number of rollers in said plurality ofrollers.
 8. The apparatus according to claim 1, further comprising:amotor having an armature rotation shaft; a casing; and an epicycle gearreduction mechanism having a sun gear formed on the armature rotationshaft, a driving shaft coaxial with the armature rotation shaft, aninternal gear disposed in the casing and surrounding a peripheralsurface of the sun gear, planetary gears rotatably supported by thedriving shaft and engaging the sun gear and the internal gear, whereinthe outer member is formed integrally with the internal gear and theinner member is formed integrally with the casing.
 9. The apparatusaccording to claim 1, further comprising:a motor having an armaturerotation shaft; a driving shaft disposed coaxially with the armaturerotation shaft; a sun gear formed on the armature rotation shaft; aninternal gear coaxial with the armature rotation shaft and surroundingthe peripheral surface of the sun gear; planetary gears engaging the sungear and the internal gear; and a planetary gear-supporting cylinderrotatably supported by the driving shaft and supporting the planetarygears such that the planetary gears rotate on the axes thereof, whereinthe outer member is formed on the planetary gear-supporting cylinder andthe inner member is formed on the driving shaft.
 10. The apparatusaccording to claim 1, wherein:the annular groove crosses the lockingconcavity, the annular groove having a radial depth deeper than that ofthe locking concavities; and the resilient member includes a resilientring fitted in the annular groove, the other periphery of the resilientring being located between a top and a bottom of the locking concave.11. The apparatus according to claim 10, wherein:an additional annulargroove is formed at an axially spaced apart location on the outerperiphery of the inner member; and an additional resilient ring isfitted in the additional annular groove the resilient ring andadditional resilient ring contacting axial ends of the roller.
 12. Theapparatus according to claim 10, wherein:the resilient ring has an endpart axially extending beyond the axial end of the roller; and an outerperipheral surface of the end part is in contact with the outer memberso that the resilient ring is restricted from deforming radiallyoutwardly.
 13. The apparatus according to claim 10, further comprising:abiasing member disposed in the wedge-shaped groove to bias the rollertoward the shallow side, wherein the resilient ring is set to benon-deformable relative to a biasing force of the biasing member. 14.The apparatus according to claim 10, further comprising:a motor havingan armature rotation shaft; and a driving shaft driven by a torquetransmission from the armature rotation shaft, wherein the outer memberand the inner member are placed between the armature rotation shaft andthe driving shaft.
 15. An apparatus comprising:an outer member and aninner member rotatable relative to each other and opposed to each otherwith a predetermined interval in a radial direction therebetween; awedge-shaped groove formed on one of an inner peripheral surface of theouter member and an outer peripheral surface of the inner member suchthat the depth of the wedge-shaped groove increases from one side to theother side in a circumferential direction: a roller movably accommodatedin the wedge-shaped groove for connecting the outer member and the innermember with each other at a shallow side of the wedge-shaped groove soas to transmit a torque and for disconnecting the outer member and theinner member from each other at a deep side of the wedge-shaped groove:a locking concavity formed on another of the inner peripheral surface ofthe outer member and the outer peripheral surface of the inner memberfor locking the inner roller thereto when the outer member and the innermember are connected with each other; a resilient member disposed onsaid another of the inner peripheral surface of the outer member and theouter peripheral surface of the inner member for shifting the roller toa position at which the roller does not contact a radial top of thelocking concavity when the outer member and the inner member aredisconnected from each other; a pair of annular grooves formedcircumferentially on the outer peripheral surface of the inner member,each annular groove having a radial depth gradually becoming deeper froman axial end of the inner member; wherein the resilient member includesresilient metal rings resiliently deformable to be received in eachannular groove.
 16. The apparatus according to claim 15, wherein:theresilient metal rings each have an inside part and an outside partaxially extending inwardly and outwardly with respect to the axial endof the roller; and radially outer peripheral surfaces of the insideparts are held in contact with the roller so that only the inside partsof the resilient rings are deformed by the roller.
 17. An apparatuscomprising:an outer member and an inner member rotatable relative toeach other and opposed to each other with a predetermined interval in aradial direction therebetween; a wedge-shaped groove formed on an innerperipheral surface of the outer member such that the depth of thewedge-shaped groove increases from one side to the other side in acircumferential direction; a roller movably accommodated in thewedge-shaped groove for connecting the outer member and the inner memberwith each other at a shallow side of the wedge-shaped groove so as totransmit a torque and for disconnecting the outer member and the innermember from each other at a deep side of the wedge-shaped groove; alocking concavity formed on the outer peripheral surface of the innermember for locking the inner roller thereto when the outer member andthe inner member are connected with each other; and a resilient memberdisposed on the outer peripheral surface of the inner member forshifting the roller to a position at which the roller does not contact aradial top of the locking concavity when the outer member and the innermember are disconnected from each other.
 18. The apparatus according toclaim 17, wherein the resilient member is disposed to keep the rolleraway from a radial bottom of the locking concavity when the roller isreceived in the locking concavity so that the outer member and the innermember are connected with each other.
 19. The apparatus according toclaim 17, wherein:at least one additional wedge-shaped groove is formedon the inner peripheral surface of the outer member, the wedge-shapedgroove and the at least one additional wedge-shaped groove forming aplurality of wedge-shaped grooves, each groove in said plurality ofwedge-shaped grooves having a corresponding roller movably accommodatedtherein; at least one additional locking concavity is formedcircumferentially on the outer peripheral surface of the inner member,the locking concavity and the at least one additional locking concavityforming a plurality of locking concavities; and the number of thelocking concavities in said plurality of locking concavities is greaterthan the number of rollers in said plurality of rollers.
 20. Theapparatus according to claim 17, wherein the roller is disposed todisengage from the locking concavity due to resiliency of the resilientmember when a torque greater than a predetermined amount is applied in atorque transmission direction.
 21. The apparatus according to claim 17,further comprising:an annular groove formed on the outer peripheralsurface of the inner member, wherein the resilient member includes aresilient ring accommodated in the annular groove.
 22. The apparatusaccording to claim 17, further comprising at least one additionalresilient member, the resilient member and the at least one additionalresilient member forming a plurality of resilient members and beingdisposed at a plurality of locations spaced apart from one other in theaxial direction of the outer member and the inner member such that theplurality of resilient members contact at least both axial sides of theroller.
 23. The apparatus according to claim 17, further comprising:anannular groove formed circumferentially on the outer peripheral surfaceof the inner member in a manner to cross the locking concave, theannular groove having a radial depth deeper than that of the lockingconcave; wherein the resilient member includes a resilient ring fittedin the annular groove, the other periphery of the resilient ring beinglocated between a top and a bottom of the locking concave.
 24. Theapparatus according to claim 23, wherein:an additional annular groove isformed at an axially spaced apart location on the outer periphery of theinner member; and an additional resilient ring is fitted in theadditional annular groove, the resilient ring and additional resilientring contacting axial ends of the roller.
 25. The apparatus according toclaim 23, wherein:the resilient ring has an end part axially extendingbeyond the axial end of the roller; and an outer peripheral surface ofthe end part is in contact with the outer member so that the resilientring is restricted from deforming radially outwardly.
 26. The apparatusaccording to claim 23, further comprising:a biasing member disposed inthe wedge-shaped groove to bias the roller toward the shallow side,wherein the resilient ring is set to be non-deformable relative to abiasing force of the biasing member.
 27. The apparatus according toclaim 23, further comprising:a motor having an armature rotation shaft;and a driving shaft driven by a torque transmission from the armaturerotation shaft, wherein the outer member and the inner member are placedbetween the armature rotation shaft and the driving shaft.